1. Field of the Invention
The present invention relates to a fixing unit position-adjusting apparatus for positioning a fixing unit which fixes a toner image on a record medium, such as a recording paper sheet, with respect to a main body of an image forming apparatus, and to an image forming apparatus.
2. Description of the Related Art
Image forming apparatuses which form an image on a recording paper sheet with an electrophotographic system have conventionally been used as copying machines, facsimile machines, and printers. Such an electrophotographic image forming apparatus charges a photoreceptor with a charging apparatus, and then forms an electrostatic latent image on the surface of the photoreceptor through such operation as optical writing performed in accordance with a document image or image information. The electrostatic latent image is then developed by a developing apparatus into a toner image with use of a toner. The toner image that is a visible image is transferred onto a recording paper sheet that is a recording medium. The recording paper sheet is then heat-pressurized by a fixing unit so that the toner image is fixed onto the recording paper sheet. Thus, copied sheets and printed sheets are obtained.
One example of the fixing unit for use in image forming apparatuses is a roller-type fixing unit made up of a heating roller having a heat source and a pressure roller that rotates in contact with the heating roller. The roller-type fixing unit applies heat and pressure to a recording paper sheet, which has been conveyed to between the heating roller and the pressure roller, to fix a toner image thereon. Another example is a belt-type fixing unit having an endless fixing belt stretched over between the heating roller and the fixing roller. The belt-type fixing unit applies heat and pressure to a recording paper sheet, which has been conveyed to between the fixing belt and the pressure roller, to fix a toner image thereon.
Image forming apparatuses are required to support a wide variety of recording paper sheets, ranging from extra large-size paper sheets that are one size larger than standardized sizes to small postcard sheets with a relatively small size as well as from super-thin paper sheets to super-thick paper sheets. At the same time, high productivity and high image quality are also required. However, it was difficult to satisfy both conveying performance and image quality for the recording paper sheets.
When the positioning accuracy of the fixing unit with respect to the recording paper sheets are poor, the recording paper sheets may enter into the fixing unit with a displaced position, which causes distorted images, generation of wrinkles, edges of the recording paper sheets being folded, and occurrence of paper jam. In such circumstances, enhanced positioning accuracy of the fixing unit is required. In response to such requirements, an adjustment mechanism is used, that adjusts a reference pin of the fixing unit in a conveyance direction.
In one example, the adjustment mechanism is adapted to fix the position of a reference pin on the rear side of the fixing unit while adjusting the position of a reference pin on the near side of the fixing unit in the conveyance direction so as to optimize the parallelism of the fixing unit with respect to the recording paper sheets.
Japanese Laid-open Patent Publication No. 2004-117395 discloses an image forming apparatus including a retract drive means for use in retracting a fixing unit into a main body of the image forming apparatus so as to set the fixing unit in the image forming apparatus. The retract drive means slides the fixing unit in a fixing unit insertion direction so that the fixing unit is retracted to and positioned at a proper position.
However, when the adjustment mechanism is provided, a parts count increases as a plurality of component members need to be added. This causes a problem of a complicated configuration of the apparatus. Similarly, in the case of providing the retract drive means described in Japanese Laid-open Patent Publication No. 2004-117395, the parts count increases as a structure for sliding the fixing unit is needed. This also causes the problem of the complicated configuration of the apparatus.
In view of the above-mentioned conventional art, there is need to provide a fixing unit position-adjusting apparatus which can position the fixing unit with a simple configuration and which can optimize the parallelism of the fixing unit with respect to recording paper sheets that enter into the fixing unit.